请教SC-PREP-139 解释看的不太明白

139.(32262-!-item-!-188;#058&006043)

On Earth, among the surest indications of sunspot cycles are believed to be the rate that trees grow, as seen in the rings visible in the cross sections of their trunks.

(A) On Earth, among the surest indications of sunspot cycles are believed to be the rate that trees grow

(B) On Earth, among the surest indications of sunspot cycles are, it is believed, the rate of tree growth

(C) On Earth, the rate at which trees grow is believed to be among the surest indications of sunspot cycles

(D) Among the surest indications on Earth of sunspot cycles, believed to be the tree growth rate

(E) Among the surest indications on Earth of sunspot cycles is believed to be the rate at which trees grow

答案是E  请问这一整句话怎么翻译？

还有C  解释说后面的their 会产生歧义我理解；但“On earth在句首修饰整个句子，不符合逻辑”，这句话不太明白。

请高手指教，多谢！

把on earth放句首表明在地球上......在其他星球上就不这样

E的翻译大概是 树的生长速率被认为是最确定的sunspots cycles的迹象（之一）

原来是 surest 最确定的，我以为是个单词，词典上还没有，汗！

谢谢！